Extremely Slow Photoconductivity Response of CH3NH3PbI3 Perovskites Suggesting Structural Changes under Working Conditions

Arie Zaban^a, Yaniv Bouhadana ^a, Shay Tirosh^a, Laxman Gouda^a, Eynav Haltzi^a, Ronen Gottesman^a, Edoardo Mosconi^b, Filippo De Angelis^b

^aBar Ilan University, Bar Ilan University, Ramat Gan, 52900, Israel

^bCNR-ISTM, via Elce di Sotto 8, Perugia, 06123, Italy

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Ronen Gottesman, 026
Publication date: 5th February 2015

Photoconductivity measurements of CH₃NH₃PbI₃ deposited between two dielectric-protected Au electrodes show extremely slow response. The CH₃NH₃PbI₃, bridging a gap of 2000 nm, was subjected to a DC bias and cycles of 5 min illumination and varying dark duration. The approach to steady-state photocurrent lasted tens of seconds with a strong dependence on the dark duration preceding the illumination. On the basis of DFT calculations, we propose that under light + bias the methylammonium ions are freed to rotate and align along the electric field, thus modifying the structure of the inorganic scaffold. While ions alignment is expected to be fast, the adjustment of the inorganic scaffold seems to last seconds as reflected in the extremely slow photoconductivity response. We propose that under working conditions a modified, photostable, perovskite structure is formed, depending on the bias and illumination parameters. Our findings seem to clarify the origin of the well-known hysteresis in perovskite solar cells.

Gottesman, R.; Haltzi, E.; Gouda, L.; Tirosh, S.; Bouhadana, Y.; Zaban, A.; Mosconi, E.; De Angelis, F. Extremely slow photo- conductivity response of CH3NH3PbI3 perovskites suggesting structural changes under working conditions. J. Phys. Chem. Lett. 2014, 5, 2662−2669.

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